https://www.raspberrypi.org/forums/viewtopic.php?p=890408#p890408

sudo apt-get install --no-install-recommends xserver-xorg xserver-xorg-legacy
sudo apt-get install --no-install-recommends xinit

#Disable avahi
#The Pi is going to use simple uni-cast DNS - multi-cast DNS support is not required.
sudo systemctl disable avahi-daemon
sudo systemctl stop avahi-daemon

#Disable TriggerHappy
#The Pi isn't being used with button. Disable the TriggerHappy daemon (not that it is a init.d service)
sudo systemctl disable triggerhappy
sudo systemctl stop triggerhappy 

#When not using nfs remove:
sudo apt-get remove –purge nfs-common

#When not using bluetooth:
sudo vi /boot/config.txt
dtoverlay=pi3-disable-bt

sudo vi /boot/cmdline.txt
change console=tty1 to console=tty3
add at the end of the line: loglevel=3 quiet logo.nologo

sudo apt-get install --no-install-recommends xserver-xorg
# sudo apt-get install xserver-xorg-input-evdev
sudo apt-get install --no-install-recommends xinit
# required for xset command
sudo apt-get install x11-xserver-utils
sudo apt-get install linphone
echo "# Disable any form of screen saver / screen blanking / power management
xset s off
xset s noblank
xset -dpms
# Allow quitting the X server with CTRL-ATL-Backspace
setxkbmap -option terminate:ctrl_alt_bksp
exec /usr/bin/linphone" | tee ~/.xinitrc

sudo dpkg-reconfigure xserver-xorg-legacy

#set anybody

echo "allowed_users=anybody
needs_root_rights=yes" | sudo tee /etc/X11/Xwrapper.config

sudo usermod -a -G audio,tty,video,users pi

Autostart X on boot-up:

sudo vi /etc/systemd/system/kiosk.service

[Unit]
Description=Kiosk

[Service]
Type=oneshot
ExecStart=/usr/bin/sudo -u user /usr/bin/startx --

[Install]
WantedBy=multi-user.target

sudo systemctl enable kiosk
sudo systemctl start kiosk